Tungsten deposition using chemical vapor deposition (CVD) techniques is an integral part of many semiconductor fabrication processes. Tungsten may be used for horizontal interconnects, vias between adjacent metal layers, contacts between a first metal layer and the devices on the silicon substrate, and through silicon vias. In a conventional tungsten deposition process, the substrate is heated to the process temperature in a deposition chamber, and a thin layer of tungsten that serves as a seed or nucleation layer is deposited. Thereafter, the remainder of the tungsten film (the bulk layer) is deposited on the nucleation layer. Conventionally, the tungsten bulk layer is formed by the reduction of tungsten hexafluoride (WF6) with hydrogen (H2). Tungsten layers deposit over an entire exposed surface area of the substrate including features and a field region.
A through-silicon via (TSV) is a vertical electrical connection passing completely through a silicon wafer or die. TSV technology is used to create 3D packages and integrated circuits (IC). It provides interconnection of vertically aligned electronic devices through internal wiring that significantly reduces complexity and overall dimensions of a multi-level electronic circuit. Tungsten is an attractive material for TSV applications because of its high electrical conductivity, resistance to electromigration, and thermal expansion coefficient comparable to that of silicon.